As shown in FIG. 31, a DC-DC converter 100 of a flyback type disclosed in Patent Document 1 stores the power stored in a leakage inductance it in a condenser C101 through a parasitic diode of a transistor Q102 and a transformer coil N103 when a transistor Q101 is turned OFF. The energy stored in the condenser C101 is output to a secondary side through a transformer T by turning ON the transistor Q102.
As shown in FIG. 32, a DC-DC converter 201 of a flyback type disclosed in Patent Document 2 has a converter circuit 203 that converts a direct-current input to alternate current so as to transmit to a primary coil of a transformer 202 arranged at the post-stage, and a rectification circuit 204 arranged at the post-stage of the transformer 202, the rectification circuit rectifying the alternate current obtained from the secondary coil of the transformer 202. In the converter circuit 203, MOSFET 209 and 210 are connected in a bridge configuration to constitute a half bridge and condensers 211 and 212 connected in series are connected in parallel to MOSFET 9 and 10. Further, the positive terminal of the primary coil of the transformer 202 is connected between the MOSFET 209 and the MOSFET 210 and the negative terminal of the primary coil of the transformer 202 is connected between the condenser 211 and the condenser 212.
When the MOSFET 210 conducts, an electric current path at the primary side passes from the condenser 212 through the transformer 202 and the MOSFET 210 to go back to the condenser 212. Also, when the MOSFET 209 conducts, the electric current path at the primary side passes from the condenser 211 through the MOSFET 209 and the transformer 202 to go back to the condenser 211.
A DC-DC converter 300 disclosed in Patent Document 3 is shown in FIG. 33. Energy stored in a transformer is stored in snubber condensers 108A and 107 when a semiconductor switch element 105A is turned OFF. The energy stored in the snubber condenser 107 is regenerated to a power supply 101 and the energy that stored in the snubber condenser 108A also refreshes to the power supply 101, by turning ON a semiconductor switch element 106B immediately before the semiconductor switch element 105A is turned ON.
In addition, there are DC-DC converters disclosed in Patent Documents 4 to 9, as other related technologies.
Patent Document 1: Japanese Unexamined Patent Publication No. 2000-262055
Patent Document 2: Japanese Unexamined Patent Publication No. 2005-269792
Patent Document 3: Japanese Unexamined Patent Publication No. 11 (1999)-146648
Patent Document 4: Japanese Unexamined Patent Publication No. 6 (1994)-261546
Patent Document 5: Japanese Unexamined Patent Publication No. 9 (1997)-312973
Patent Document 6: Japanese Unexamined Patent Publication No. 11 (1999)-225473
Patent Document 7: Japanese Unexamined Patent Publication No. 11 (1999)-356045
Patent Document 8: Japanese Unexamined Patent Publication No. 5 (1993)-64448
Patent Document 9: Japanese Unexamined Patent Publication No. 8 (1996)-107677